Retinal hypoxia is increasingly being implicated as a factor in the pathogenesis of various retinal vasculitidies including diabetic retinopathy. The in vivo measurement of oxygen in intraocular tissue has been made possible with the development of the oxygen microelectrode. Using an oxygen microelectrode, the relative contributions of the retinal and choroidal circulations to the oxygen supply of the retina of various animals will be determined. In an attempt to control the retinal oxygen supply, the ocular circulation will be altered using physiological and pharmacological methods. A model of retinal hypoxia will be produced in these animals by photocoagulating a branch retinal vein. Attempts will be made to regulate the oxygen supply to the areas of hypoxia. The effects of scatter retinal photocoagulation in the area of hypoxia will be studied by correlating the retinal oxygen tension, the local electroretinogram,and fluorescein angiograms, both before and after photocoagulation. It is hoped that long-term studies of this animal model of retinal hypoxia secondary to branch retinal vein occlusion will help elucidate the factors that contribute to retinal neovascularization.